Pd catalyst supported on CeO₂ nanotubes with enhanced structural stability toward oxidative carbonylation of phenol

Ordered CeO₂ nanotubes (CeO₂-T) were prepared via a hydrothermal synthesis process using the triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide (P123) as a morphology control agent. CeO₂-T characterization demonstrated the formation of single crystal structures having lengths between 1-3 μm and diameters < 100 nm. A supported Pd catalyst (Pd/CeO₂-T) was also prepared through hydrothermal means. H₂-temperature reduction profile and Raman spectroscopy analyses showed that the oxygen vacancies on the CeO₂ surface increased and the reduction temperature of the surface oxygen decreased after Pd loading onto CeO₂-T. Pd/CeO₂-T was employed as a catalyst toward the oxidative carbonylation of phenol and the reaction conditions were optimized. Phenol conversion was 53.2% with 96.7% selectivity to diphenyl carbonate under optimal conditions. The integrity of the tubular CeO₂ structure was maintained after the catalyst was recycled, however, both activity and selectivity significantly decreased, which was mainly attributed to the Pd active component significantly leaching during the reaction.